The invention relates to a method and a device for monitoring a plurality of sensors detecting a process, and the process may notably be an xe2x80x9cElectronic Stability Programxe2x80x9d (ESP) for vehicles.
Electronic stability programs of this type are driving-dynamics control systems for vehicles which are used to assist the driver in critical driving situations during braking, accelerating and steering, and to intervene where the driver himself/herself has no direct intervention possibility. The control system assists the driver when braking, especially on a roadway with a low or varying coefficient of friction, on which the vehicle might be no longer steerable due to locking wheels or might start to skid; it further assists in accelerating, there being the risk of spinning of the driven wheels, and finally when steering during cornering, where the vehicle might oversteer or understeer. In total, not only the comfort but also the active safety will be improved considerably.
A control system of this type is based on a closed-loop control circuit which, during normal operation of the vehicle, takes over typical control tasks and is intended to stabilize the vehicle as quickly as possible in extreme driving situations. Sensors to sense the various driving-dynamics parameters are of special importance as generators of actual values. The precondition for a plausible control is that the sensors correctly represent the actual condition of the controlled system. This is particularly important in driving stability control operations in extreme driving situations, where a control deviation must be adjusted by the control already within a very short time. This is the reason why the ESP sensors (yaw rate sensor, transverse acceleration sensor, steering angle sensor) of an electronic Stability program require constant monitoring in order to detect faults, in the sensors at an early point of time and rule out a faulty control which might cause a vehicle condition that is critical in terms of safety.
ESP sensors may e.g. suffer from so-called connecting errors. These errors cause malfunctions which involve that the sensors permanently indicate constant values in their useful range so that driving dynamics cannot be represented correctly. It cannot be ruled out in certain driving stiuations with low dynamics that such a connecting error stays undiscovered.
In view of the above, an object of the present invention is to provide a method and a device for monitoring a plurality of sensors detecting a process, such as an electronic stability program (ESP) for vehicles, which permits considerably reducing the risk of a wrong measurement due to connecting errors of the sensors.
This object is achieved by means of a method of the above-mentioned type which is characterized by the following steps: detecting time variations of the output signals of the sensors, comparing and checking the variations in view of their plausibility, which is determined by the dependencies of the sensor output signals caused by the process, and producing an error message. In the absence of plausibility.
Further, this object is achieved by a device which includes a connecting error detection unit with a first device for detecting time variations of the output signals of the sensors and a second device for comparing and checking the variations in view of their plausibility which is determined by the dependencies of the sensor output signals caused by the process, and producing an error message in the absence of plausibility.
In a particularly favorable manner, the present invention can be combined with an ESP system for vehicles which is controlled by a microprocessor unit, wherein the process is the electronic driving stability program, and the sensors comprise a yaw rate sensor, a transverse acceleration sensor, and a steering angle sensor, and the first and second device is implemented by a subprogram in the microprocessor unit.
The present invention is especially suited for the combination with a model-based monitoring of the sensors of an electronic stability program (ESP) for vehicles which is described in the parallel application No. 199 29 155.1 and by reference herewith shall be made a part of the disclosure of this invention. In that system, respectively one of the sensors is monitored in that its output signal is compared with analytical reference values (redundancies) which are determined by means of a multi-process model from process reference variables or process measured variables that are not monitored currently. However, even with this system it cannot be fully excluded that the connecting errors explained hereinabove will remain undiscovered. The present invention provides a remedy for these cases.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawing.